Polyurethane foams having improved flame-retardant properties have long been sought and, because flammability requirements are becoming increasingly more stringent, continue to receive attention. As a result, particular attention has recently been paid to the British Furniture and Furnishings Fire Safety Regulations of Consumer Protection 1988/no. 1324, which imposes particularly stringent demands on flammability resistance of the foams. In this test, a wooden crib weighing 17 g is filled with a certain amount of isopropyl alcohol and ignited on a chair frame finished with the foam. The flames must die within 10 minutes and the weight loss should be no more than 60 g. This test imposes particularly strict requirements on the foams in respect of the ignition resistance thereof. In addition to the more stringent flame resistance requirements, restricted use of phosphate esters or haloalkyl phosphate esters as flameproofing agents is being urged.
Another approach to flameproofing polyurethane foams uses melamine as a flameproofing agent. In this regard, see German Offenlegungsschrift 2,809,084, British Patent 2,177,406, German Offenlegungsschrift 3,530,519, German Offenlegungsschrift 2,815,554, and British Patent 2,094,315. However, it has now been found that melamine still does not impart adequate flameproofing to polyurethane foam under long-term use, even when trischloroethyl phosphate or other phosphates, for example, are used as additional flameproofing agents. This disadvantage is overcome by the process of the present invention.